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A309117 Number of perfect matchings on a triangular lattice of width 4 and length n. 0
1, 1, 5, 15, 56, 203, 749, 2777, 10293, 38240, 141997, 527593, 1960029, 7282483, 27057400, 100531559, 373522965, 1387822193, 5156442953, 19158736256, 71184183353, 264484479633, 982690786037, 3651182836279, 13565952140920, 50404229548515, 187276671274621 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..26.

S. N. Perepechko, Number of perfect matchings on triangular lattices of fixed width, DIMA'2015 slides.

FORMULA

G.f.: (1-z)*(1+z)*(1-z-5*z^2-z^3+z^4)/((1+z-3*z^2-3*z^3+z^4)*(1-3*z-3*z^2+z^3+z^4)).

CROSSREFS

Cf. A011900, A307349.

Sequence in context: A137959 A001552 A165731 * A307349 A203294 A149589

Adjacent sequences:  A309114 A309115 A309116 * A309118 A309119 A309120

KEYWORD

nonn,easy

AUTHOR

Sergey Perepechko, Jul 13 2019

STATUS

approved

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Last modified May 28 17:37 EDT 2020. Contains 334684 sequences. (Running on oeis4.)